Sexually transmitted infections (STI) are important causes of morbidity among American adolescents. Recurrent infections with N. gonorrhoeae, C. trachomatis and T. vaginalis are common; reinfection increases the risk of morbidity and thus contributes importantly to the public health burden of sexual transmitted disease. STI among adolescents take place within the context of psychosocial development, self-protective behaviors, social environment and sexual interpersonal relationships but these contexts are given inadequate attention in traditional epidemiologic models and interventions to reduce STI. Supported by social-psychological theory, adolescent behavioral research, and extensive clinical experience with sexually active adolescents, the proposed research is intended to expand current understanding of the behavioral epidemiology of recurrent sexually transmitted infections among adolescents by careful exploration of the central role of protective behaviors within the context of sexual interpersonal relationships and partner change characteristics. The Specific Aims are to: 1) Describe behavioral, interpersonal and organism- specific factors associated with risk of recurrent STI in adolescent males and females; 2) Assess actors associated with the timing of recurrent infections to test the specific hypothesis that early (within 6 months of initial infection) recurrences are more likely to occur in the setting of an ongoing sexual relationship, and that late (more than 6 months after initial infection) recurrence is more likely to occur in the setting of new sexual partners. We will enroll and follow for 15 months a cohort of 600 high risk males and females, 14-19 year old, with STI (N. gonorrhoeae, C trachomatis, and T. vaginalis) obtaining trimonthly serial behavioral measures and genitourinary tract cultures. As related to the timing of subsequent infection(s), we will determine the variations in and patterns of accrual of sexual partnerships (with special attention to the duration, pattern and rate of change of relationships), the inter- and intra-personal factors which underlie these patterns, the interrelationships among behaviors which modify risk for STI (health protective vs health endangering such as condom use, long-term monogamous relationship, substance use) and the association of social environment with recurrent STI. Framed within Self-Efficacy Theory, the results of this behavioral epidemiologic study of high risk adolescents will be directly relevant to future interventions to reduce recurrent STI among high risk adolescents.